* Re: [PATCH] KVM: s390: introduce module parameter kvm.use_gisa
2020-02-27 9:10 [PATCH] KVM: s390: introduce module parameter kvm.use_gisa Michael Mueller
@ 2020-02-27 9:26 ` David Hildenbrand
2020-02-27 12:04 ` Michael Mueller
2020-02-27 9:47 ` Cornelia Huck
` (2 subsequent siblings)
3 siblings, 1 reply; 14+ messages in thread
From: David Hildenbrand @ 2020-02-27 9:26 UTC (permalink / raw)
To: Michael Mueller, borntraeger, frankja; +Cc: kvm, cohuck, thuth, linux-s390
On 27.02.20 10:10, Michael Mueller wrote:
> The boolean module parameter "kvm.use_gisa" controls if newly
> created guests will use the GISA facility if provided by the
> host system. The default is yes.
>
> # cat /sys/module/kvm/parameters/use_gisa
> Y
>
> The parameter can be changed on the fly.
>
> # echo N > /sys/module/kvm/parameters/use_gisa
>
> Already running guests are not affected by this change.
>
> The kvm s390 debug feature shows if a guest is running with GISA.
>
> # grep gisa /sys/kernel/debug/s390dbf/kvm-$pid/sprintf
> 00 01582725059:843303 3 - 08 00000000e119bc01 gisa 0x00000000c9ac2642 initialized
> 00 01582725059:903840 3 - 11 000000004391ee22 00[0000000000000000-0000000000000000]: AIV gisa format-1 enabled for cpu 000
> ...
> 00 01582725059:916847 3 - 08 0000000094fff572 gisa 0x00000000c9ac2642 cleared
>
> In general, that value should not be changed as the GISA facility
> enhances interruption delivery performance.
>
> A reason to switch the GISA facility off might be a performance
> comparison run or debugging.
>
> Signed-off-by: Michael Mueller <mimu@linux.ibm.com>
> ---
> arch/s390/kvm/kvm-s390.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index d7ff30e45589..5c2081488024 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -184,6 +184,11 @@ static u8 halt_poll_max_steal = 10;
> module_param(halt_poll_max_steal, byte, 0644);
> MODULE_PARM_DESC(halt_poll_max_steal, "Maximum percentage of steal time to allow polling");
>
> +/* if set to true, the GISA will be initialized and used if available */
> +static bool use_gisa = true;
> +module_param(use_gisa, bool, 0644);
> +MODULE_PARM_DESC(use_gisa, "Use the GISA if the host supports it.");
> +
> /*
> * For now we handle at most 16 double words as this is what the s390 base
> * kernel handles and stores in the prefix page. If we ever need to go beyond
> @@ -2504,7 +2509,8 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
> kvm->arch.use_skf = sclp.has_skey;
> spin_lock_init(&kvm->arch.start_stop_lock);
> kvm_s390_vsie_init(kvm);
> - kvm_s390_gisa_init(kvm);
> + if (use_gisa)
> + kvm_s390_gisa_init(kvm);
Looks sane to me. gi->origin will remain NULL and act like
css_general_characteristics.aiv wouldn't be around.
I assume initializing the gib is fine, and having some guests use it and
others not?
I do wonder if it would be even clearer/cleaner to not allow to change
this property on the fly, and to also not init the gib if disabled.
If you want to perform performance tests, simply unload+reload KVM.
--
Thanks,
David / dhildenb
^ permalink raw reply [flat|nested] 14+ messages in thread* Re: [PATCH] KVM: s390: introduce module parameter kvm.use_gisa
2020-02-27 9:26 ` David Hildenbrand
@ 2020-02-27 12:04 ` Michael Mueller
2020-02-27 12:31 ` David Hildenbrand
0 siblings, 1 reply; 14+ messages in thread
From: Michael Mueller @ 2020-02-27 12:04 UTC (permalink / raw)
To: David Hildenbrand, borntraeger, frankja; +Cc: kvm, cohuck, thuth, linux-s390
On 27.02.20 10:26, David Hildenbrand wrote:
> On 27.02.20 10:10, Michael Mueller wrote:
>> The boolean module parameter "kvm.use_gisa" controls if newly
>> created guests will use the GISA facility if provided by the
>> host system. The default is yes.
>>
>> # cat /sys/module/kvm/parameters/use_gisa
>> Y
>>
>> The parameter can be changed on the fly.
>>
>> # echo N > /sys/module/kvm/parameters/use_gisa
>>
>> Already running guests are not affected by this change.
>>
>> The kvm s390 debug feature shows if a guest is running with GISA.
>>
>> # grep gisa /sys/kernel/debug/s390dbf/kvm-$pid/sprintf
>> 00 01582725059:843303 3 - 08 00000000e119bc01 gisa 0x00000000c9ac2642 initialized
>> 00 01582725059:903840 3 - 11 000000004391ee22 00[0000000000000000-0000000000000000]: AIV gisa format-1 enabled for cpu 000
>> ...
>> 00 01582725059:916847 3 - 08 0000000094fff572 gisa 0x00000000c9ac2642 cleared
>>
>> In general, that value should not be changed as the GISA facility
>> enhances interruption delivery performance.
>>
>> A reason to switch the GISA facility off might be a performance
>> comparison run or debugging.
>>
>> Signed-off-by: Michael Mueller <mimu@linux.ibm.com>
>> ---
>> arch/s390/kvm/kvm-s390.c | 8 +++++++-
>> 1 file changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index d7ff30e45589..5c2081488024 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -184,6 +184,11 @@ static u8 halt_poll_max_steal = 10;
>> module_param(halt_poll_max_steal, byte, 0644);
>> MODULE_PARM_DESC(halt_poll_max_steal, "Maximum percentage of steal time to allow polling");
>>
>> +/* if set to true, the GISA will be initialized and used if available */
>> +static bool use_gisa = true;
>> +module_param(use_gisa, bool, 0644);
>> +MODULE_PARM_DESC(use_gisa, "Use the GISA if the host supports it.");
>> +
>> /*
>> * For now we handle at most 16 double words as this is what the s390 base
>> * kernel handles and stores in the prefix page. If we ever need to go beyond
>> @@ -2504,7 +2509,8 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>> kvm->arch.use_skf = sclp.has_skey;
>> spin_lock_init(&kvm->arch.start_stop_lock);
>> kvm_s390_vsie_init(kvm);
>> - kvm_s390_gisa_init(kvm);
>> + if (use_gisa)
>> + kvm_s390_gisa_init(kvm);
>
> Looks sane to me. gi->origin will remain NULL and act like
> css_general_characteristics.aiv wouldn't be around.
right
>
> I assume initializing the gib is fine, and having some guests use it and
> others not?
Is fine as well.
>
> I do wonder if it would be even clearer/cleaner to not allow to change
> this property on the fly, and to also not init the gib if disabled.
>
> If you want to perform performance tests, simply unload+reload KVM.
That would work if kvm is build as module but not in-kernel, then
a reboot would be required with kvm.use_gisa=Y/N
I tend to leave it as it is.
Thanks,
Michael
>
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH] KVM: s390: introduce module parameter kvm.use_gisa
2020-02-27 12:04 ` Michael Mueller
@ 2020-02-27 12:31 ` David Hildenbrand
2020-02-27 12:57 ` Michael Mueller
0 siblings, 1 reply; 14+ messages in thread
From: David Hildenbrand @ 2020-02-27 12:31 UTC (permalink / raw)
To: mimu, borntraeger, frankja; +Cc: kvm, cohuck, thuth, linux-s390
On 27.02.20 13:04, Michael Mueller wrote:
>
>
> On 27.02.20 10:26, David Hildenbrand wrote:
>> On 27.02.20 10:10, Michael Mueller wrote:
>>> The boolean module parameter "kvm.use_gisa" controls if newly
>>> created guests will use the GISA facility if provided by the
>>> host system. The default is yes.
>>>
>>> # cat /sys/module/kvm/parameters/use_gisa
>>> Y
>>>
>>> The parameter can be changed on the fly.
>>>
>>> # echo N > /sys/module/kvm/parameters/use_gisa
>>>
>>> Already running guests are not affected by this change.
>>>
>>> The kvm s390 debug feature shows if a guest is running with GISA.
>>>
>>> # grep gisa /sys/kernel/debug/s390dbf/kvm-$pid/sprintf
>>> 00 01582725059:843303 3 - 08 00000000e119bc01 gisa 0x00000000c9ac2642 initialized
>>> 00 01582725059:903840 3 - 11 000000004391ee22 00[0000000000000000-0000000000000000]: AIV gisa format-1 enabled for cpu 000
>>> ...
>>> 00 01582725059:916847 3 - 08 0000000094fff572 gisa 0x00000000c9ac2642 cleared
>>>
>>> In general, that value should not be changed as the GISA facility
>>> enhances interruption delivery performance.
>>>
>>> A reason to switch the GISA facility off might be a performance
>>> comparison run or debugging.
>>>
>>> Signed-off-by: Michael Mueller <mimu@linux.ibm.com>
>>> ---
>>> arch/s390/kvm/kvm-s390.c | 8 +++++++-
>>> 1 file changed, 7 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>>> index d7ff30e45589..5c2081488024 100644
>>> --- a/arch/s390/kvm/kvm-s390.c
>>> +++ b/arch/s390/kvm/kvm-s390.c
>>> @@ -184,6 +184,11 @@ static u8 halt_poll_max_steal = 10;
>>> module_param(halt_poll_max_steal, byte, 0644);
>>> MODULE_PARM_DESC(halt_poll_max_steal, "Maximum percentage of steal time to allow polling");
>>>
>>> +/* if set to true, the GISA will be initialized and used if available */
>>> +static bool use_gisa = true;
>>> +module_param(use_gisa, bool, 0644);
>>> +MODULE_PARM_DESC(use_gisa, "Use the GISA if the host supports it.");
>>> +
>>> /*
>>> * For now we handle at most 16 double words as this is what the s390 base
>>> * kernel handles and stores in the prefix page. If we ever need to go beyond
>>> @@ -2504,7 +2509,8 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>>> kvm->arch.use_skf = sclp.has_skey;
>>> spin_lock_init(&kvm->arch.start_stop_lock);
>>> kvm_s390_vsie_init(kvm);
>>> - kvm_s390_gisa_init(kvm);
>>> + if (use_gisa)
>>> + kvm_s390_gisa_init(kvm);
>>
>> Looks sane to me. gi->origin will remain NULL and act like
>> css_general_characteristics.aiv wouldn't be around.
>
> right
>
>>
>> I assume initializing the gib is fine, and having some guests use it and
>> others not?
>
> Is fine as well.
>
>>
>> I do wonder if it would be even clearer/cleaner to not allow to change
>> this property on the fly, and to also not init the gib if disabled.
>>
>> If you want to perform performance tests, simply unload+reload KVM.
>
> That would work if kvm is build as module but not in-kernel, then
Right, but AFAIK that's not an usual setup (at least in distros) - and
for testing purposes not an issue as well.
Anyhow, I'm fine with this
Reviewed-by: David Hildenbrand <david@redhat.com>
Thanks!
--
Thanks,
David / dhildenb
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH] KVM: s390: introduce module parameter kvm.use_gisa
2020-02-27 12:31 ` David Hildenbrand
@ 2020-02-27 12:57 ` Michael Mueller
0 siblings, 0 replies; 14+ messages in thread
From: Michael Mueller @ 2020-02-27 12:57 UTC (permalink / raw)
To: David Hildenbrand, borntraeger, frankja; +Cc: kvm, cohuck, thuth, linux-s390
On 27.02.20 13:31, David Hildenbrand wrote:
> On 27.02.20 13:04, Michael Mueller wrote:
>>
>>
>> On 27.02.20 10:26, David Hildenbrand wrote:
>>> On 27.02.20 10:10, Michael Mueller wrote:
>>>> The boolean module parameter "kvm.use_gisa" controls if newly
>>>> created guests will use the GISA facility if provided by the
>>>> host system. The default is yes.
>>>>
>>>> # cat /sys/module/kvm/parameters/use_gisa
>>>> Y
>>>>
>>>> The parameter can be changed on the fly.
>>>>
>>>> # echo N > /sys/module/kvm/parameters/use_gisa
>>>>
>>>> Already running guests are not affected by this change.
>>>>
>>>> The kvm s390 debug feature shows if a guest is running with GISA.
>>>>
>>>> # grep gisa /sys/kernel/debug/s390dbf/kvm-$pid/sprintf
>>>> 00 01582725059:843303 3 - 08 00000000e119bc01 gisa 0x00000000c9ac2642 initialized
>>>> 00 01582725059:903840 3 - 11 000000004391ee22 00[0000000000000000-0000000000000000]: AIV gisa format-1 enabled for cpu 000
>>>> ...
>>>> 00 01582725059:916847 3 - 08 0000000094fff572 gisa 0x00000000c9ac2642 cleared
>>>>
>>>> In general, that value should not be changed as the GISA facility
>>>> enhances interruption delivery performance.
>>>>
>>>> A reason to switch the GISA facility off might be a performance
>>>> comparison run or debugging.
>>>>
>>>> Signed-off-by: Michael Mueller <mimu@linux.ibm.com>
>>>> ---
>>>> arch/s390/kvm/kvm-s390.c | 8 +++++++-
>>>> 1 file changed, 7 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>>>> index d7ff30e45589..5c2081488024 100644
>>>> --- a/arch/s390/kvm/kvm-s390.c
>>>> +++ b/arch/s390/kvm/kvm-s390.c
>>>> @@ -184,6 +184,11 @@ static u8 halt_poll_max_steal = 10;
>>>> module_param(halt_poll_max_steal, byte, 0644);
>>>> MODULE_PARM_DESC(halt_poll_max_steal, "Maximum percentage of steal time to allow polling");
>>>>
>>>> +/* if set to true, the GISA will be initialized and used if available */
>>>> +static bool use_gisa = true;
>>>> +module_param(use_gisa, bool, 0644);
>>>> +MODULE_PARM_DESC(use_gisa, "Use the GISA if the host supports it.");
>>>> +
>>>> /*
>>>> * For now we handle at most 16 double words as this is what the s390 base
>>>> * kernel handles and stores in the prefix page. If we ever need to go beyond
>>>> @@ -2504,7 +2509,8 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>>>> kvm->arch.use_skf = sclp.has_skey;
>>>> spin_lock_init(&kvm->arch.start_stop_lock);
>>>> kvm_s390_vsie_init(kvm);
>>>> - kvm_s390_gisa_init(kvm);
>>>> + if (use_gisa)
>>>> + kvm_s390_gisa_init(kvm);
>>>
>>> Looks sane to me. gi->origin will remain NULL and act like
>>> css_general_characteristics.aiv wouldn't be around.
>>
>> right
>>
>>>
>>> I assume initializing the gib is fine, and having some guests use it and
>>> others not?
>>
>> Is fine as well.
>>
>>>
>>> I do wonder if it would be even clearer/cleaner to not allow to change
>>> this property on the fly, and to also not init the gib if disabled.
>>>
>>> If you want to perform performance tests, simply unload+reload KVM.
>>
>> That would work if kvm is build as module but not in-kernel, then
>
> Right, but AFAIK that's not an usual setup (at least in distros) - and
> for testing purposes not an issue as well.
>
> Anyhow, I'm fine with this
>
> Reviewed-by: David Hildenbrand <david@redhat.com>
>
Thank you!
> Thanks!
>
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH] KVM: s390: introduce module parameter kvm.use_gisa
2020-02-27 9:10 [PATCH] KVM: s390: introduce module parameter kvm.use_gisa Michael Mueller
2020-02-27 9:26 ` David Hildenbrand
@ 2020-02-27 9:47 ` Cornelia Huck
2020-02-27 12:19 ` Michael Mueller
2020-02-27 12:27 ` Christian Borntraeger
2020-02-27 16:23 ` Christian Borntraeger
3 siblings, 1 reply; 14+ messages in thread
From: Cornelia Huck @ 2020-02-27 9:47 UTC (permalink / raw)
To: Michael Mueller; +Cc: borntraeger, frankja, kvm, david, thuth, linux-s390
On Thu, 27 Feb 2020 10:10:31 +0100
Michael Mueller <mimu@linux.ibm.com> wrote:
> The boolean module parameter "kvm.use_gisa" controls if newly
> created guests will use the GISA facility if provided by the
> host system. The default is yes.
>
> # cat /sys/module/kvm/parameters/use_gisa
> Y
>
> The parameter can be changed on the fly.
>
> # echo N > /sys/module/kvm/parameters/use_gisa
>
> Already running guests are not affected by this change.
>
> The kvm s390 debug feature shows if a guest is running with GISA.
>
> # grep gisa /sys/kernel/debug/s390dbf/kvm-$pid/sprintf
> 00 01582725059:843303 3 - 08 00000000e119bc01 gisa 0x00000000c9ac2642 initialized
> 00 01582725059:903840 3 - 11 000000004391ee22 00[0000000000000000-0000000000000000]: AIV gisa format-1 enabled for cpu 000
> ...
> 00 01582725059:916847 3 - 08 0000000094fff572 gisa 0x00000000c9ac2642 cleared
Maybe log something as well if it is off due to this kernel parameter?
>
> In general, that value should not be changed as the GISA facility
> enhances interruption delivery performance.
>
> A reason to switch the GISA facility off might be a performance
> comparison run or debugging.
>
> Signed-off-by: Michael Mueller <mimu@linux.ibm.com>
> ---
> arch/s390/kvm/kvm-s390.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index d7ff30e45589..5c2081488024 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -184,6 +184,11 @@ static u8 halt_poll_max_steal = 10;
> module_param(halt_poll_max_steal, byte, 0644);
> MODULE_PARM_DESC(halt_poll_max_steal, "Maximum percentage of steal time to allow polling");
>
> +/* if set to true, the GISA will be initialized and used if available */
> +static bool use_gisa = true;
> +module_param(use_gisa, bool, 0644);
> +MODULE_PARM_DESC(use_gisa, "Use the GISA if the host supports it.");
I probably would have inverted the logic (i.e. introduce a disable_gisa
parameter that is off by default), as you want KVM to use the gisa,
except in special circumstances.
> +
> /*
> * For now we handle at most 16 double words as this is what the s390 base
> * kernel handles and stores in the prefix page. If we ever need to go beyond
> @@ -2504,7 +2509,8 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
> kvm->arch.use_skf = sclp.has_skey;
> spin_lock_init(&kvm->arch.start_stop_lock);
> kvm_s390_vsie_init(kvm);
> - kvm_s390_gisa_init(kvm);
> + if (use_gisa)
> + kvm_s390_gisa_init(kvm);
I assume we're fine with no gisa but a gib (i.e. doesn't hurt?)
> KVM_EVENT(3, "vm 0x%pK created by pid %u", kvm, current->pid);
>
> return 0;
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH] KVM: s390: introduce module parameter kvm.use_gisa
2020-02-27 9:47 ` Cornelia Huck
@ 2020-02-27 12:19 ` Michael Mueller
0 siblings, 0 replies; 14+ messages in thread
From: Michael Mueller @ 2020-02-27 12:19 UTC (permalink / raw)
To: Cornelia Huck; +Cc: borntraeger, frankja, kvm, david, thuth, linux-s390
On 27.02.20 10:47, Cornelia Huck wrote:
> On Thu, 27 Feb 2020 10:10:31 +0100
> Michael Mueller <mimu@linux.ibm.com> wrote:
>
>> The boolean module parameter "kvm.use_gisa" controls if newly
>> created guests will use the GISA facility if provided by the
>> host system. The default is yes.
>>
>> # cat /sys/module/kvm/parameters/use_gisa
>> Y
>>
>> The parameter can be changed on the fly.
>>
>> # echo N > /sys/module/kvm/parameters/use_gisa
>>
>> Already running guests are not affected by this change.
>>
>> The kvm s390 debug feature shows if a guest is running with GISA.
>>
>> # grep gisa /sys/kernel/debug/s390dbf/kvm-$pid/sprintf
>> 00 01582725059:843303 3 - 08 00000000e119bc01 gisa 0x00000000c9ac2642 initialized
>> 00 01582725059:903840 3 - 11 000000004391ee22 00[0000000000000000-0000000000000000]: AIV gisa format-1 enabled for cpu 000
>> ...
>> 00 01582725059:916847 3 - 08 0000000094fff572 gisa 0x00000000c9ac2642 cleared
>
> Maybe log something as well if it is off due to this kernel parameter?
There is also no message when the host does not support it.
>
>>
>> In general, that value should not be changed as the GISA facility
>> enhances interruption delivery performance.
>>
>> A reason to switch the GISA facility off might be a performance
>> comparison run or debugging.
>>
>> Signed-off-by: Michael Mueller <mimu@linux.ibm.com>
>> ---
>> arch/s390/kvm/kvm-s390.c | 8 +++++++-
>> 1 file changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index d7ff30e45589..5c2081488024 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -184,6 +184,11 @@ static u8 halt_poll_max_steal = 10;
>> module_param(halt_poll_max_steal, byte, 0644);
>> MODULE_PARM_DESC(halt_poll_max_steal, "Maximum percentage of steal time to allow polling");
>>
>> +/* if set to true, the GISA will be initialized and used if available */
>> +static bool use_gisa = true;
>> +module_param(use_gisa, bool, 0644);
>> +MODULE_PARM_DESC(use_gisa, "Use the GISA if the host supports it.");
>
> I probably would have inverted the logic (i.e. introduce a disable_gisa
> parameter that is off by default), as you want KVM to use the gisa,
> except in special circumstances.
Hm, in my opinion "use it := no" is more explicit and natural
than "don't use it := yes"
>
>> +
>> /*
>> * For now we handle at most 16 double words as this is what the s390 base
>> * kernel handles and stores in the prefix page. If we ever need to go beyond
>> @@ -2504,7 +2509,8 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>> kvm->arch.use_skf = sclp.has_skey;
>> spin_lock_init(&kvm->arch.start_stop_lock);
>> kvm_s390_vsie_init(kvm);
>> - kvm_s390_gisa_init(kvm);
>> + if (use_gisa)
>> + kvm_s390_gisa_init(kvm);
>
> I assume we're fine with no gisa but a gib (i.e. doesn't hurt?)
The GIB is a host entity and is required for guests with GISA that want
to use AP with interruptions in guest.
>
>> KVM_EVENT(3, "vm 0x%pK created by pid %u", kvm, current->pid);
>>
>> return 0;
>
Thanks a lot!
Michael
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH] KVM: s390: introduce module parameter kvm.use_gisa
2020-02-27 9:10 [PATCH] KVM: s390: introduce module parameter kvm.use_gisa Michael Mueller
2020-02-27 9:26 ` David Hildenbrand
2020-02-27 9:47 ` Cornelia Huck
@ 2020-02-27 12:27 ` Christian Borntraeger
2020-02-27 12:43 ` Michael Mueller
2020-02-27 12:48 ` Cornelia Huck
2020-02-27 16:23 ` Christian Borntraeger
3 siblings, 2 replies; 14+ messages in thread
From: Christian Borntraeger @ 2020-02-27 12:27 UTC (permalink / raw)
To: Michael Mueller, frankja; +Cc: kvm, cohuck, david, thuth, linux-s390
On 27.02.20 10:10, Michael Mueller wrote:
> The boolean module parameter "kvm.use_gisa" controls if newly
> created guests will use the GISA facility if provided by the
> host system. The default is yes.
>
> # cat /sys/module/kvm/parameters/use_gisa
> Y
>
> The parameter can be changed on the fly.
>
> # echo N > /sys/module/kvm/parameters/use_gisa
>
> Already running guests are not affected by this change.
>
> The kvm s390 debug feature shows if a guest is running with GISA.
>
> # grep gisa /sys/kernel/debug/s390dbf/kvm-$pid/sprintf
> 00 01582725059:843303 3 - 08 00000000e119bc01 gisa 0x00000000c9ac2642 initialized
> 00 01582725059:903840 3 - 11 000000004391ee22 00[0000000000000000-0000000000000000]: AIV gisa format-1 enabled for cpu 000
> ...
> 00 01582725059:916847 3 - 08 0000000094fff572 gisa 0x00000000c9ac2642 cleared
>
> In general, that value should not be changed as the GISA facility
> enhances interruption delivery performance.
>
> A reason to switch the GISA facility off might be a performance
> comparison run or debugging.
>
> Signed-off-by: Michael Mueller <mimu@linux.ibm.com>
Looks good to me. Regarding the other comments, I think allowing for dynamic changes
and keeping use_gisa vs disable_gisa makes sense. So I would think that the patch
as is makes sense.
The only question is: shall we set use_gisa to 0 when the machine does not support
it (e.g. VSIE?) and then also forbid setting it to 1? Could be overkill.
> ---
> arch/s390/kvm/kvm-s390.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index d7ff30e45589..5c2081488024 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -184,6 +184,11 @@ static u8 halt_poll_max_steal = 10;
> module_param(halt_poll_max_steal, byte, 0644);
> MODULE_PARM_DESC(halt_poll_max_steal, "Maximum percentage of steal time to allow polling");
>
> +/* if set to true, the GISA will be initialized and used if available */
> +static bool use_gisa = true;
> +module_param(use_gisa, bool, 0644);
> +MODULE_PARM_DESC(use_gisa, "Use the GISA if the host supports it.");
> +
> /*
> * For now we handle at most 16 double words as this is what the s390 base
> * kernel handles and stores in the prefix page. If we ever need to go beyond
> @@ -2504,7 +2509,8 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
> kvm->arch.use_skf = sclp.has_skey;
> spin_lock_init(&kvm->arch.start_stop_lock);
> kvm_s390_vsie_init(kvm);
> - kvm_s390_gisa_init(kvm);
> + if (use_gisa)
> + kvm_s390_gisa_init(kvm);
> KVM_EVENT(3, "vm 0x%pK created by pid %u", kvm, current->pid);
>
> return 0;
>
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH] KVM: s390: introduce module parameter kvm.use_gisa
2020-02-27 12:27 ` Christian Borntraeger
@ 2020-02-27 12:43 ` Michael Mueller
2020-02-27 13:24 ` Christian Borntraeger
2020-02-27 12:48 ` Cornelia Huck
1 sibling, 1 reply; 14+ messages in thread
From: Michael Mueller @ 2020-02-27 12:43 UTC (permalink / raw)
To: Christian Borntraeger, frankja; +Cc: kvm, cohuck, david, thuth, linux-s390
On 27.02.20 13:27, Christian Borntraeger wrote:
>
>
> On 27.02.20 10:10, Michael Mueller wrote:
>> The boolean module parameter "kvm.use_gisa" controls if newly
>> created guests will use the GISA facility if provided by the
>> host system. The default is yes.
>>
>> # cat /sys/module/kvm/parameters/use_gisa
>> Y
>>
>> The parameter can be changed on the fly.
>>
>> # echo N > /sys/module/kvm/parameters/use_gisa
>>
>> Already running guests are not affected by this change.
>>
>> The kvm s390 debug feature shows if a guest is running with GISA.
>>
>> # grep gisa /sys/kernel/debug/s390dbf/kvm-$pid/sprintf
>> 00 01582725059:843303 3 - 08 00000000e119bc01 gisa 0x00000000c9ac2642 initialized
>> 00 01582725059:903840 3 - 11 000000004391ee22 00[0000000000000000-0000000000000000]: AIV gisa format-1 enabled for cpu 000
>> ...
>> 00 01582725059:916847 3 - 08 0000000094fff572 gisa 0x00000000c9ac2642 cleared
>>
>> In general, that value should not be changed as the GISA facility
>> enhances interruption delivery performance.
>>
>> A reason to switch the GISA facility off might be a performance
>> comparison run or debugging.
>>
>> Signed-off-by: Michael Mueller <mimu@linux.ibm.com>
>
> Looks good to me. Regarding the other comments, I think allowing for dynamic changes
> and keeping use_gisa vs disable_gisa makes sense. So I would think that the patch
> as is makes sense.
>
> The only question is: shall we set use_gisa to 0 when the machine does not support
> it (e.g. VSIE?) and then also forbid setting it to 1? Could be overkill.
Then I would rename the parameter to "try_to_use_gisa" instead. (a joke
;) )
In that case we exit gisa_init() because of the missing AIV facility.
void kvm_s390_gisa_init(struct kvm *kvm)
{
struct kvm_s390_gisa_interrupt *gi = &kvm->arch.gisa_int;
--> if (!css_general_characteristics.aiv)
return;
gi->origin = &kvm->arch.sie_page2->gisa;
gi->alert.mask = 0;
...
}
Thanks,
Michael
>
>
>> ---
>> arch/s390/kvm/kvm-s390.c | 8 +++++++-
>> 1 file changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index d7ff30e45589..5c2081488024 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -184,6 +184,11 @@ static u8 halt_poll_max_steal = 10;
>> module_param(halt_poll_max_steal, byte, 0644);
>> MODULE_PARM_DESC(halt_poll_max_steal, "Maximum percentage of steal time to allow polling");
>>
>> +/* if set to true, the GISA will be initialized and used if available */
>> +static bool use_gisa = true;
>> +module_param(use_gisa, bool, 0644);
>> +MODULE_PARM_DESC(use_gisa, "Use the GISA if the host supports it.");
>> +
>> /*
>> * For now we handle at most 16 double words as this is what the s390 base
>> * kernel handles and stores in the prefix page. If we ever need to go beyond
>> @@ -2504,7 +2509,8 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>> kvm->arch.use_skf = sclp.has_skey;
>> spin_lock_init(&kvm->arch.start_stop_lock);
>> kvm_s390_vsie_init(kvm);
>> - kvm_s390_gisa_init(kvm);
>> + if (use_gisa)
>> + kvm_s390_gisa_init(kvm);
>> KVM_EVENT(3, "vm 0x%pK created by pid %u", kvm, current->pid);
>>
>> return 0;
>>
>
--
Mit freundlichen Grüßen / Kind regards
Michael Müller
IBM Deutschland Research & Development GmbH
Vorsitzender des Aufsichtsrats: Gregor Pillen
Geschäftsführung: Dirk Wittkopp
Sitz der Gesellschaft: Böblingen
Registergericht: Amtsgericht Stuttgart, HRB 243294
^ permalink raw reply [flat|nested] 14+ messages in thread* Re: [PATCH] KVM: s390: introduce module parameter kvm.use_gisa
2020-02-27 12:43 ` Michael Mueller
@ 2020-02-27 13:24 ` Christian Borntraeger
2020-02-27 16:10 ` Michael Mueller
0 siblings, 1 reply; 14+ messages in thread
From: Christian Borntraeger @ 2020-02-27 13:24 UTC (permalink / raw)
To: mimu, frankja; +Cc: kvm, cohuck, david, thuth, linux-s390
On 27.02.20 13:43, Michael Mueller wrote:
>
>
> On 27.02.20 13:27, Christian Borntraeger wrote:
>>
>>
>> On 27.02.20 10:10, Michael Mueller wrote:
>>> The boolean module parameter "kvm.use_gisa" controls if newly
>>> created guests will use the GISA facility if provided by the
>>> host system. The default is yes.
>>>
>>> # cat /sys/module/kvm/parameters/use_gisa
>>> Y
>>>
>>> The parameter can be changed on the fly.
>>>
>>> # echo N > /sys/module/kvm/parameters/use_gisa
>>>
>>> Already running guests are not affected by this change.
>>>
>>> The kvm s390 debug feature shows if a guest is running with GISA.
>>>
>>> # grep gisa /sys/kernel/debug/s390dbf/kvm-$pid/sprintf
>>> 00 01582725059:843303 3 - 08 00000000e119bc01 gisa 0x00000000c9ac2642 initialized
>>> 00 01582725059:903840 3 - 11 000000004391ee22 00[0000000000000000-0000000000000000]: AIV gisa format-1 enabled for cpu 000
>>> ...
>>> 00 01582725059:916847 3 - 08 0000000094fff572 gisa 0x00000000c9ac2642 cleared
>>>
>>> In general, that value should not be changed as the GISA facility
>>> enhances interruption delivery performance.
>>>
>>> A reason to switch the GISA facility off might be a performance
>>> comparison run or debugging.
>>>
>>> Signed-off-by: Michael Mueller <mimu@linux.ibm.com>
>>
>> Looks good to me. Regarding the other comments, I think allowing for dynamic changes
>> and keeping use_gisa vs disable_gisa makes sense. So I would think that the patch
>> as is makes sense.
>>
>> The only question is: shall we set use_gisa to 0 when the machine does not support
>> it (e.g. VSIE?) and then also forbid setting it to 1? Could be overkill.
>
> Then I would rename the parameter to "try_to_use_gisa" instead. (a joke ;) )
>
> In that case we exit gisa_init() because of the missing AIV facility.
>
> void kvm_s390_gisa_init(struct kvm *kvm)
> {
> struct kvm_s390_gisa_interrupt *gi = &kvm->arch.gisa_int;
>
> --> if (!css_general_characteristics.aiv)
> return;
> gi->origin = &kvm->arch.sie_page2->gisa;
> gi->alert.mask = 0;
> ...
> }
>
I know. My point was more: "can we expose this". But this is probably overkill.
^ permalink raw reply [flat|nested] 14+ messages in thread* Re: [PATCH] KVM: s390: introduce module parameter kvm.use_gisa
2020-02-27 13:24 ` Christian Borntraeger
@ 2020-02-27 16:10 ` Michael Mueller
0 siblings, 0 replies; 14+ messages in thread
From: Michael Mueller @ 2020-02-27 16:10 UTC (permalink / raw)
To: Christian Borntraeger, frankja; +Cc: kvm, cohuck, david, thuth, linux-s390
On 27.02.20 14:24, Christian Borntraeger wrote:
>
>
> On 27.02.20 13:43, Michael Mueller wrote:
>>
>>
>> On 27.02.20 13:27, Christian Borntraeger wrote:
>>>
>>>
>>> On 27.02.20 10:10, Michael Mueller wrote:
>>>> The boolean module parameter "kvm.use_gisa" controls if newly
>>>> created guests will use the GISA facility if provided by the
>>>> host system. The default is yes.
>>>>
>>>> # cat /sys/module/kvm/parameters/use_gisa
>>>> Y
>>>>
>>>> The parameter can be changed on the fly.
>>>>
>>>> # echo N > /sys/module/kvm/parameters/use_gisa
>>>>
>>>> Already running guests are not affected by this change.
>>>>
>>>> The kvm s390 debug feature shows if a guest is running with GISA.
>>>>
>>>> # grep gisa /sys/kernel/debug/s390dbf/kvm-$pid/sprintf
>>>> 00 01582725059:843303 3 - 08 00000000e119bc01 gisa 0x00000000c9ac2642 initialized
>>>> 00 01582725059:903840 3 - 11 000000004391ee22 00[0000000000000000-0000000000000000]: AIV gisa format-1 enabled for cpu 000
>>>> ...
>>>> 00 01582725059:916847 3 - 08 0000000094fff572 gisa 0x00000000c9ac2642 cleared
>>>>
>>>> In general, that value should not be changed as the GISA facility
>>>> enhances interruption delivery performance.
>>>>
>>>> A reason to switch the GISA facility off might be a performance
>>>> comparison run or debugging.
>>>>
>>>> Signed-off-by: Michael Mueller <mimu@linux.ibm.com>
>>>
>>> Looks good to me. Regarding the other comments, I think allowing for dynamic changes
>>> and keeping use_gisa vs disable_gisa makes sense. So I would think that the patch
>>> as is makes sense.
>>>
>>> The only question is: shall we set use_gisa to 0 when the machine does not support
>>> it (e.g. VSIE?) and then also forbid setting it to 1? Could be overkill.
>>
>> Then I would rename the parameter to "try_to_use_gisa" instead. (a joke ;) )
>>
>> In that case we exit gisa_init() because of the missing AIV facility.
>>
>> void kvm_s390_gisa_init(struct kvm *kvm)
>> {
>> struct kvm_s390_gisa_interrupt *gi = &kvm->arch.gisa_int;
>>
>> --> if (!css_general_characteristics.aiv)
>> return;
>> gi->origin = &kvm->arch.sie_page2->gisa;
>> gi->alert.mask = 0;
>> ...
>> }
>>
>
> I know. My point was more: "can we expose this". But this is probably overkill.
I agree with Connie here, that would make the whole thing
just more error-prone. That way the messages are at least
consistent.
>
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH] KVM: s390: introduce module parameter kvm.use_gisa
2020-02-27 12:27 ` Christian Borntraeger
2020-02-27 12:43 ` Michael Mueller
@ 2020-02-27 12:48 ` Cornelia Huck
2020-02-27 12:56 ` Michael Mueller
1 sibling, 1 reply; 14+ messages in thread
From: Cornelia Huck @ 2020-02-27 12:48 UTC (permalink / raw)
To: Christian Borntraeger
Cc: Michael Mueller, frankja, kvm, david, thuth, linux-s390
On Thu, 27 Feb 2020 13:27:10 +0100
Christian Borntraeger <borntraeger@de.ibm.com> wrote:
> On 27.02.20 10:10, Michael Mueller wrote:
> > The boolean module parameter "kvm.use_gisa" controls if newly
> > created guests will use the GISA facility if provided by the
> > host system. The default is yes.
> >
> > # cat /sys/module/kvm/parameters/use_gisa
> > Y
> >
> > The parameter can be changed on the fly.
> >
> > # echo N > /sys/module/kvm/parameters/use_gisa
> >
> > Already running guests are not affected by this change.
> >
> > The kvm s390 debug feature shows if a guest is running with GISA.
> >
> > # grep gisa /sys/kernel/debug/s390dbf/kvm-$pid/sprintf
> > 00 01582725059:843303 3 - 08 00000000e119bc01 gisa 0x00000000c9ac2642 initialized
> > 00 01582725059:903840 3 - 11 000000004391ee22 00[0000000000000000-0000000000000000]: AIV gisa format-1 enabled for cpu 000
> > ...
> > 00 01582725059:916847 3 - 08 0000000094fff572 gisa 0x00000000c9ac2642 cleared
> >
> > In general, that value should not be changed as the GISA facility
> > enhances interruption delivery performance.
> >
> > A reason to switch the GISA facility off might be a performance
> > comparison run or debugging.
> >
> > Signed-off-by: Michael Mueller <mimu@linux.ibm.com>
>
> Looks good to me. Regarding the other comments, I think allowing for dynamic changes
> and keeping use_gisa vs disable_gisa makes sense. So I would think that the patch
> as is makes sense.
use_gisa vs disable_gisa is more a personal preference; I don't mind
keeping it as use_gisa.
>
> The only question is: shall we set use_gisa to 0 when the machine does not support
> it (e.g. VSIE?) and then also forbid setting it to 1? Could be overkill.
I don't think you should try to overload a debug knob like that; it's
now simple enough, adding more code also adds to the potential for
errors.
>
>
> > ---
> > arch/s390/kvm/kvm-s390.c | 8 +++++++-
> > 1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> > index d7ff30e45589..5c2081488024 100644
> > --- a/arch/s390/kvm/kvm-s390.c
> > +++ b/arch/s390/kvm/kvm-s390.c
> > @@ -184,6 +184,11 @@ static u8 halt_poll_max_steal = 10;
> > module_param(halt_poll_max_steal, byte, 0644);
> > MODULE_PARM_DESC(halt_poll_max_steal, "Maximum percentage of steal time to allow polling");
> >
> > +/* if set to true, the GISA will be initialized and used if available */
> > +static bool use_gisa = true;
> > +module_param(use_gisa, bool, 0644);
> > +MODULE_PARM_DESC(use_gisa, "Use the GISA if the host supports it.");
Especially as the description explicitly says "if the host supports it"
-- that's good enough for a new knob.
> > +
> > /*
> > * For now we handle at most 16 double words as this is what the s390 base
> > * kernel handles and stores in the prefix page. If we ever need to go beyond
> > @@ -2504,7 +2509,8 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
> > kvm->arch.use_skf = sclp.has_skey;
> > spin_lock_init(&kvm->arch.start_stop_lock);
> > kvm_s390_vsie_init(kvm);
> > - kvm_s390_gisa_init(kvm);
> > + if (use_gisa)
> > + kvm_s390_gisa_init(kvm);
> > KVM_EVENT(3, "vm 0x%pK created by pid %u", kvm, current->pid);
> >
> > return 0;
> >
>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH] KVM: s390: introduce module parameter kvm.use_gisa
2020-02-27 12:48 ` Cornelia Huck
@ 2020-02-27 12:56 ` Michael Mueller
0 siblings, 0 replies; 14+ messages in thread
From: Michael Mueller @ 2020-02-27 12:56 UTC (permalink / raw)
To: Cornelia Huck, Christian Borntraeger
Cc: frankja, kvm, david, thuth, linux-s390
On 27.02.20 13:48, Cornelia Huck wrote:
> On Thu, 27 Feb 2020 13:27:10 +0100
> Christian Borntraeger <borntraeger@de.ibm.com> wrote:
>
>> On 27.02.20 10:10, Michael Mueller wrote:
>>> The boolean module parameter "kvm.use_gisa" controls if newly
>>> created guests will use the GISA facility if provided by the
>>> host system. The default is yes.
>>>
>>> # cat /sys/module/kvm/parameters/use_gisa
>>> Y
>>>
>>> The parameter can be changed on the fly.
>>>
>>> # echo N > /sys/module/kvm/parameters/use_gisa
>>>
>>> Already running guests are not affected by this change.
>>>
>>> The kvm s390 debug feature shows if a guest is running with GISA.
>>>
>>> # grep gisa /sys/kernel/debug/s390dbf/kvm-$pid/sprintf
>>> 00 01582725059:843303 3 - 08 00000000e119bc01 gisa 0x00000000c9ac2642 initialized
>>> 00 01582725059:903840 3 - 11 000000004391ee22 00[0000000000000000-0000000000000000]: AIV gisa format-1 enabled for cpu 000
>>> ...
>>> 00 01582725059:916847 3 - 08 0000000094fff572 gisa 0x00000000c9ac2642 cleared
>>>
>>> In general, that value should not be changed as the GISA facility
>>> enhances interruption delivery performance.
>>>
>>> A reason to switch the GISA facility off might be a performance
>>> comparison run or debugging.
>>>
>>> Signed-off-by: Michael Mueller <mimu@linux.ibm.com>
>>
>> Looks good to me. Regarding the other comments, I think allowing for dynamic changes
>> and keeping use_gisa vs disable_gisa makes sense. So I would think that the patch
>> as is makes sense.
>
> use_gisa vs disable_gisa is more a personal preference; I don't mind
> keeping it as use_gisa.
>
>>
>> The only question is: shall we set use_gisa to 0 when the machine does not support
>> it (e.g. VSIE?) and then also forbid setting it to 1? Could be overkill.
>
> I don't think you should try to overload a debug knob like that; it's
> now simple enough, adding more code also adds to the potential for
> errors.
>
>>
>>
>>> ---
>>> arch/s390/kvm/kvm-s390.c | 8 +++++++-
>>> 1 file changed, 7 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>>> index d7ff30e45589..5c2081488024 100644
>>> --- a/arch/s390/kvm/kvm-s390.c
>>> +++ b/arch/s390/kvm/kvm-s390.c
>>> @@ -184,6 +184,11 @@ static u8 halt_poll_max_steal = 10;
>>> module_param(halt_poll_max_steal, byte, 0644);
>>> MODULE_PARM_DESC(halt_poll_max_steal, "Maximum percentage of steal time to allow polling");
>>>
>>> +/* if set to true, the GISA will be initialized and used if available */
>>> +static bool use_gisa = true;
>>> +module_param(use_gisa, bool, 0644);
>>> +MODULE_PARM_DESC(use_gisa, "Use the GISA if the host supports it.");
>
> Especially as the description explicitly says "if the host supports it"
> -- that's good enough for a new knob.
>
>>> +
>>> /*
>>> * For now we handle at most 16 double words as this is what the s390 base
>>> * kernel handles and stores in the prefix page. If we ever need to go beyond
>>> @@ -2504,7 +2509,8 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>>> kvm->arch.use_skf = sclp.has_skey;
>>> spin_lock_init(&kvm->arch.start_stop_lock);
>>> kvm_s390_vsie_init(kvm);
>>> - kvm_s390_gisa_init(kvm);
>>> + if (use_gisa)
>>> + kvm_s390_gisa_init(kvm);
>>> KVM_EVENT(3, "vm 0x%pK created by pid %u", kvm, current->pid);
>>>
>>> return 0;
>>>
>>
>
> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
>
Thanks!
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH] KVM: s390: introduce module parameter kvm.use_gisa
2020-02-27 9:10 [PATCH] KVM: s390: introduce module parameter kvm.use_gisa Michael Mueller
` (2 preceding siblings ...)
2020-02-27 12:27 ` Christian Borntraeger
@ 2020-02-27 16:23 ` Christian Borntraeger
3 siblings, 0 replies; 14+ messages in thread
From: Christian Borntraeger @ 2020-02-27 16:23 UTC (permalink / raw)
To: Michael Mueller, frankja; +Cc: kvm, cohuck, david, thuth, linux-s390
On 27.02.20 10:10, Michael Mueller wrote:
> The boolean module parameter "kvm.use_gisa" controls if newly
> created guests will use the GISA facility if provided by the
> host system. The default is yes.
>
> # cat /sys/module/kvm/parameters/use_gisa
> Y
>
> The parameter can be changed on the fly.
>
> # echo N > /sys/module/kvm/parameters/use_gisa
>
> Already running guests are not affected by this change.
>
> The kvm s390 debug feature shows if a guest is running with GISA.
>
> # grep gisa /sys/kernel/debug/s390dbf/kvm-$pid/sprintf
> 00 01582725059:843303 3 - 08 00000000e119bc01 gisa 0x00000000c9ac2642 initialized
> 00 01582725059:903840 3 - 11 000000004391ee22 00[0000000000000000-0000000000000000]: AIV gisa format-1 enabled for cpu 000
> ...
> 00 01582725059:916847 3 - 08 0000000094fff572 gisa 0x00000000c9ac2642 cleared
>
> In general, that value should not be changed as the GISA facility
> enhances interruption delivery performance.
>
> A reason to switch the GISA facility off might be a performance
> comparison run or debugging.
>
> Signed-off-by: Michael Mueller <mimu@linux.ibm.com>
Thanks applied.
^ permalink raw reply [flat|nested] 14+ messages in thread